In Recent years, wireless communication devices, such as cellular phones, notebook computers, and the like are more popular to promote the importance of antennas that are capable of transmitting and receiving signals. Therefore, antennas with simple structure have become increasingly popular, especially ones which operate on the principle of inverted-F antennas.
U.S. Pat. No. 6,812,892 discloses a conventional antenna. Please refer to FIG. 1, which illustrates a conventional antenna 1′ including a radiating portion 2′, a connection portion 3′, and a ground portion 4′. The connection portion 3′ including a first segment 31′, a second segment 32′, and a third segment 33′ is connected to the radiating portion 2′, the ground portion 4′, and a feeder line 5′. Transmitting signals from the feeder line 5′ passes through an input point P′ on the first segment 31′ to radiating portion 2′. Thus, the input point P′ divides the radiating portion 2′ into a first radiating portion 21′ and a second radiating portion 22′, so that the radiating portion 2′ forms two PIFAs operating in a higher and a lower frequency bands.
The main characteristic of conventional antenna 1′ is based on matching impedance and resonating in specific frequency bands, so that the connection portion 3′ has a complex structure. Referring to FIG. 1, there are one turn between the first segment 31′ and the second segment 32′, and the other turn between the second segment 32′ and the third segment 33′. The two-turn structure causes the connection portion 3′ to have a complex stair-like structure.
The feeder line 5′ which is a coaxial cable includes a core line 51′ and a metal braided layer 52′. The core line 51′ is connected to the input point P′ of the first segment 31′. The input point P′ is adjustable, but its position is still restricted on the first segment 31′. Furthermore, the metal braided layer 52′ is soldered on the ground portion 4′ for grounding the antenna 1′. The distance between the solder point of the metal braided layer 52′ and the input point P′ is predetermined to achieve a desired matching impedance for two distinct frequency bands.
It is noted that the efficiency of the conventional antenna 1′ depends on the structure of the connection portion 3′ and the input point P′. However, the connection portion 3′ with a complex stair-like structure is not only restricts the position of the input point P′, but also the bandwidth of the conventional antenna 1′.
Accordingly, there should be an antenna for solving the above problems, simplifying a structure, and having a wider bandwidth.
Therefore, it is tried to rectify those drawbacks and provide an antenna that has a simpler structure and is more adjustable for matching impedance to have a wider bandwidth. The present invention provides a dual band antenna in order to achieve the foresaid objective.